The use of mineral fillers such as silica in polymer compounds is well known.
Particulate mineral fillers can be used to reduce the cost of compounds and to improve certain physical properties. However, incompatability between the filler and polymer can restrict the use of certain fillers. In particular, it is difficult to properly incorporate silica into some polymer compounds.
Many previous attempts have been made to improve the properties of silica-reinforced compounds.
For example, U.S. Pat. No. 4,150,014 discloses a process whereby the use of an amine additive is shown to enhance the preparation of silica-filled vulcanizates of a rubbery hydroxyl-functionalized polymer.
U.S. Pat. No. 4,152,308 describes silica filled rubbery vulcanizates which are prepared using an organic acid additive, or an organic acid salt additive.
U.S. Pat. No. 4,179,421 shows that silica filled vulcanizates may be prepared from polymers which contain epoxy functionality.
The above prior art processes generally require either a functionalized polymer, or a combination of a functionalized polymer plus a further additive in order to obtain optimum incorporation of the silica filler.
Finally, U.S. Pat. No. 4,608,401 teaches a process for completely encapsulating a water insoluble particle, which may be silica, using a polymer that is free of ionically changed groups.
Heretobefore, there have not been disclosed silica reinforced compounds of a vinyl chloride resin and a nitrile rubber, wherein the compounds are characterized by containing silica which is coated with an acrylate polymer.
The compositions of the present invention surprisingly demonstrate outstanding resistance to crack growth, as measured by ASTM D813.